A known nozzle plate (German Patent Application No. 43 28 418) has a holder plate with a stepped through-bore, where the segment of this bore which lies towards the supply side, and has a smaller diameter, forms the supply opening. An injection plate is inserted into the bore segment with the larger diameter, which plate has a recess in its edge region assigned to the exit side, forming a ring channel together with a recess in the holder plate assigned to it, which channel is connected with the supply opening via slits provided in the side of the injection plate facing the supply opening. The exit-side edges of the recesses in the holder plate and the injection plate delimit a ring-shaped exit opening of the known nozzle plate.
German patent application No. 44 04 021.0 describes another nozzle plate, composed of two parts, in which a ring channel is provided between the two parts, which channel is connected with a fuel supply region via supply bores provided in the first part, and connected with a fuel exit region via a ring gap. The ring gap, in this connection, is delimited by two mantle surfaces in the shape of truncated cones, with the one being attached to the first part of the nozzle plate and the other to the second part.
The two parts of this nozzle plate are produced by galvanic second-casting of corresponding negative molds, consisting of conductive plastic, where the galvanically cast parts can be mechanically finished and subsequently attached to each other by means of gluing, diffusion soldering, or diffusion welding.
Such nozzle plates with ring gap nozzles are used in fuel injection valves for gasoline engines in order to achieve better atomization of the fuel. In this connection, the fuel is supposed to exit as a cohesive laminar jet in the shape of a conical mantle. Because of the radial expanse along the conical mantle, the fuel film becomes thinner with an increasing diameter towards the exit, until it bursts into very small droplets due to aerodynamic forces. In this manner, it is possible to achieve distribution of the fuel over a relatively large volume.
In order to obtain a uniform laminar jet, uniform pressure distribution and a uniform fuel supply are necessary at the ring gap.
The nozzle plate according to the present invention, has the advantage, in contrast, that it is possible to achieve a uniform, cohesive laminar jet in the shape of a conical mantle at the fuel discharge, by-means of the cylindrical formation of the ring channel, with a cross-section which narrows in the region of the exit opening, without an arrangement of the ring gap itself in the shape of a conical mantle being necessary. In this connection, the formation of the ring gap, according to the present invention, results in an improved flow behavior of the fuel in the nozzle plate itself, and in a more uniform formation of the laminar jet.
It is particularly advantageous if two exit openings arranged concentric to one another are provided, where each of the exit openings has its own flow path assigned to it, since this makes it possible to achieve two fuel jets in the shape of a conical mantle, which have a smaller conical angle and break down into smaller fuel droplets over a shorter path length.
With the exit opening, which is lens-shaped in a top view, it is possible to form the fuel jet which is sprayed out in such a way, in advantageous manner, that the fuel flow is divided into two partial flows. This makes it possible, for example, to supply both intake valves of a four-valve engine at the same time.
Another advantage of the present invention consists of the fact that because of the holder ridges arranged between the supply openings, the inner segment which delimits the flow path on the inside can be connected with the ring-shaped segment of the nozzle plate which delimits the flow path on the outside, in a stable manner, without the fuel flow being hampered by the nozzle plate.
In this connection, the supply openings and the holder ridges located between them can also be provided outside the diameter of the ring-shaped exit opening and therefore radially outside the ring gap, which makes it possible to enlarge the flow cross-section of the flow path through the nozzle plate on the supply side, in order to make the flow through the nozzle plate even more uniform.
The method for the production of a nozzle plate has the advantage, in this connection, that the nozzle plate can be made in one piece using this method, so that none of the joining processes which influence the formation of the ring gap, such as gluing, soldering or welding, have to be carried out on the nozzle plate.
In advantageous manner, it is possible to produce the width of the ring gap precisely, by second-casting of a single cavity mold, and it does not depend on the precision with which the connection between two parts is produced. In particular, tolerances in joining and welding together two parts are eliminated. Another advantage consists of the fact that the nozzle plate can be produced with two ring gaps which serve as exit openings, each with its own flow path, without significant additional effort.
A particular advantage of the method according to the present invention consists of the fact that the die for the production of the cavity mold can easily be produced by mechanical lathing work, e.g. with a diamond-tipped tool, with great precision. The slant of the inside wall of the ring gap, which is necessary for formation of the laminar jet to discharge the fuel, can be produced with great precision, by finishing a die part from the outside.